1. Field of the Invention
This invention relates to an improvement of a writing instrument provided with check valve means for preventing back-flow of writing ink.
2. Description of the Prior Art
This type of writing instrument is disclosed in Japanese utility model application No 4752/1993 which was laid-open under Provisionary Publication No 64956/1994 on Sep. 13, 1994.
The conventional writing instrument includes an elongated barrel having an ink-passageway formed therein, a valve room provided at a portion of the ink-passageway, a valve ball received within the valve room, and a writing tip communicating with the ink-passageway. The valve room is formed into a polygonal shape in cross-section which allows a surface of the valve room to substantially come into contact with the valve ball. A plurality of spaced apart projections for restricting movement of the valve ball in a direction toward the writing tip are provided around a portion of the polygonal valve room which is adjacent a tip end of the barrel. Each of the projections projects inwardly from corresponding one of sides of the portion of the polygonal valve room and has a tip end parallel to the corresponding side of the portion of the polygonal valve room.
In the conventional writing instrument, when a user causes the writing tip of the writing instrument to face downwardly in order to write utilizing the writing instrument, the valve ball falls toward the projections while coming into contact with sides of the valve room, and is stopped against the projections. At this time, ink from an ink reservoir housed within the barrel passes through clearances between regions of the valve ball and regions of the valve room which do not come into contact with each other, and is supplied to the writing tip. However, with the conventional writing instrument, each of such clearances is very small, so that feeding of ink to the writing tip can not be smoothly performed and it is therefore impossible to sufficiently feed ink to the writing tip.